The U.S. patent application Ser. No. 09/079,481 filed May 15, 1998, now U.S. Pat. No. 6,053,371, assigned to our assignee, discloses a meritorious liquid dispenser comprising a hollow body and a one-piece plunger including an actuator portion and piston portion. The disclosure of this patent is incorporated hereinto by reference. The plunger includes a stem and an enlarged piston head at its lower end. Between the stem and head is formed an upwardly facing shoulder. Inlet and outlet check valves are provided and a spring urges the plunger upward. The body has near the upper end an internal inward and downward flap which, when engaged by the shoulder, stops upward movement of the plunger. A vent hole is formed in the body. The flap, being above the vent hole is in position to seal venting. While the arrangement of the patent application is indeed meritorious, there has been a need for an improved vent seal particularly in lockdown position.